Packaging boxes conventionally used in the food trade are generally made of a cardboard blank, cut out, bent and cemented. Such boxes conventionally are not usable in industry and for the distribution of foodstuffs because of their cost of production and filling. Moreover, this type of package does not permit the enclosed product to be seen.
There have been developed boxes that are entirely of transparent or translucent material, permitting overall direct viewing of the contained product.
However, such boxes are not suitable for high-class contents such as for example pastries, because of their poor and relatively cheap appearance.
It is thus preferred to use boxes whose bottom is of cardboard and on which has been placed a transparent film or cover arranged to fit onto the bottom.
So as to obtain viewing of the contents, the cover can comprise a window on top closed by a transparent or translucent film. The cover can also be made entirely of transparent or translucent plastic material. However, in this latter case, the production of such covers and their emplacement are not easy. Moreover, there is not always obtained a locked closure of said cover on the bottom, the cover being simply placed over the bottom.
There has been proposed, in Belgian patent BE-A-572 970, a box constituted of a bottom on which is disposed and locked a cover having a shape corresponding to the opening of the bottom of the box and which comprises two flaps articulated on opposite corners of the cover. These flaps can cover totally the side faces of the bottom and thus have respectively an edge of their own disposed below the bottom, the bottom thus having on its side surfaces retaining plates whose lower portion extends below the bottom so as each to constitute a retaining element in which can be fixed the flexible edge of each flap of the cover provided with a groove adjacent of the bend between the flap and the edge.
According to another embodiment, in the absence of a retaining plate, the edge is bent into V-shape and is disposed below the bottom or else a retaining plate is provided along all the lengths of the lateral surface to serve as an abutment to the free end of the edge bent in a V. The articulated flaps can also partially cover the lateral surfaces of the bottom and more precisely the upper edge of said lateral surfaces. These flaps thus have an edge co-acting with an edge of the opening of the bottom by the horizontally projecting opening of the bottom provided at the upper end of the lateral surfaces.
In this type of box, it is thus necessary, to obtain good closure, to provide locking means for the flaps carried by the bottom which are always projecting from one lateral surface either at its upper end or at its lower end. These locking means provided on a corner of a lateral surface of the bottom are not always simple to make.